Efficient low emission gas turbine engines are a goal of the gas turbine industry. In particular, NOx emissions are regulated by government agencies and international agreements. Similarly, particulate matter emissions can be limited by government regulatory bodies. In order to reduce emissions from gas turbines, staged, lean burn combustors have been implemented. Staged burn combustors refer to combustor's having a staged fuel system where a first stage of fuel injectors is on during a portion of the engine operational envelope and other fuel stages are turned on and off to respond to operational requirements.
As a result of the staged fuel injections, fuel may remain stagnant in the fuel line and injector nozzles of a stage different portions of the operational envelope. The stagnant fuel may be exposed to extreme temperatures and can cause coking within the fuel line of the injector nozzle. Coking is the formation of a carbonous matter in the fuel, and the coking can result in clogged fuel nozzles, decreased efficiency and damage to the fuel nozzles themselves.